The present invention relates to a method of manufacturing a polarization surface-emitting laser, and, more particularly, to such a manufacturing method which includes changing the refractivity of a compound semiconductor mirror layer of a surface-emitting laser depending on its polarization, using the electro-optic effect of compound semiconductor materials such as GaAs and applying an electric field thereto.
Currently, surface-emitting lasers are being studied for their effective coupling with optical fibers and simple 2-dimensional (2-D) array manufacturing, in the fields of optical communications and optical information processing. For such applications of surface-emitting lasers, polarized switching is desirable since switching at high speed is possible without non-linear effects such as chirping, because such applications have stable polarization features and are performed at the state when state change, such as carrier density, in minimized in resonators.
Also, conventional polarization control methods of surface-emitting lasers include a structure which includes an asymmetrical transverse resonator having asymmetrical stress, a birefringent polarization plate and which uses quantum gain materials. However, known methods can not actively convert all the polarization of oscillating beams, due to the nature of fixed polarization in each polarizing element, and therefore only partially improves polarization.
FIG. 1 is a cross sectional view of a vertical structure of a known surface-emitting laser substrate, and may be described as follows.
A bottom mirror layer 2 is formed on a semiconductor substrate 1, and an active layer 3 is formed on bottom mirror layer 2. A top mirror layer 4 is formed on active layer 3. As the surface-emitting laser of such structure has a symmetrical structure on its light emitting surface, it will not allow polarization of the emitted light, but instead shows polarization by asymmetry generated in the process, stress effect and electric field effect for current injection. However, as these effects occur naturally, i.e. under normal operation of the lasers, and are not uniform, the problem of showing a change in polarization for each element and each output exists.
Accordingly, the present invention is directed to a method of manufacturing a substrate for surface-emitting lasers, which can control polarizations artificially and actively, by overcoming non-uniform polarization features for each element and non-uniform output generated due to an asymmetry of process, stress asymmetry and electric field effect.
To achieve the above object, polarization switching surface-emitting lasers according to the present invention have a bottom mirror layer and an active layer successively formed on top of a semiconductor substrate. A first top mirror layer of a double layer of AlAs and GaAs is formed as a column in an established and selected area on top of the active layer. An insulation area is formed at an established depth on the exposed side of the AlAs layer and second and third top mirror layers are formed as a column in a selected area of the first top mirror layer. A first n-type electrode is formed on the back of a semiconductor substrate and a p-type electrode is formed in the selected area on top of the first top mirror layer. A second n-type electrode is formed on top of the third top mirror layer. The laser is operated by applying currents between the first n-type electrode and the p-type electrode; and switching polarization by applying an electric field to the second n-type electrode formed on top of the third top mirror layer.
The manufacturing method of a polarization surface-emitting laser according to the present invention includes successively forming a bottom mirror layer and an active layer on top of a semiconductor substrate. Then, a first top mirror layer of a structure of an AlAs layer/a GaAs layer is formed on top of the active layer; and a second top mirror layer of a multi-layer structure of a distributed Bragg reflector is formed with no doping so that a high electric field may be applied to the top of the first top mirror layer thereby resulting in high reflectance. A third top mirror layer of a multi-layer structure of a distributed Bragg reflector with n-type doping so that an electric field may be efficiently distributed is formed on top of the second top mirror layer. A bottom n-type electrode is formed in the exposed area of the semiconductor substrate after coating an anti-reflection film on the back surface of the semiconductor substrate and selectively etching a part of an edge of the anti-reflection film. A laser column is formed by etching the third top mirror layer, the second mirror layer and a part of the GaAs layer of the first top mirror layer by ion beam etching after forming a photoresist pattern on the top surface of the third top mirror layer. A protective film is formed using SiNx on the entire structure including the laser column. The protective film and the first top mirror layer are etched after forming a photoresist pattern so that the laser column may be formed in the center of the device. An insulation area is formed by oxidizing the exposed AlAs layer on the side of the etched first top mirror layer by wet oxidation. A part of the protective film on top of the GaAs layer of the protective film on top of the GaAs layer of the first top mirror layer is removed, and a p-type electrode is formed on the exposed GaAs layer. The protective film on top of the laser column is then removed to form an n-type electrode on top of the exposed laser column. An insulation film is formed using SiOx or SiNx on top of the entire structure, and an electrode pad for wire bonding is formed after etching a part of the insulation film on top of the n-type electrode and the insulation film on top of the p-type electrode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.